The present invention relates to a magnetic recording/reproducing device such as a hard disk device and particularly to a magnetic recording/reproducing device using a composite head.
A magnetic recording/reproducing device such as a hard disk device is frequently used as an outer storage device having a large, which is capable of accessing at random. In recent years, high recording density for enlarging storage capacity has been greatly demanded, and the study and development have been made in various angles to meet the demand.
Generally, in the hard disk device, a plurality of magnetic disks, each which is formed on a non-magnetic substrate to have a magnetic layer, are stacked on one rotation spindle. A head for recording/reproducing is attached to an arm to be opposite to each disk surface. The arm is moved to a radial direction of the disk so that the head is positioned. In other words, a seek operation is executed. At a signal recording/reproducing time, the head slightly floats, and is placed to access to a predetermined position of the disk surface in such a state without directly contacting the disk surface rotating at high speed. Then, a signal is recorded onto a concentric track on the disk surface by the head, or the recorded signal is reproduced.
In order to meet the demand of high recording density for enlarging storage capacity, various trials have been made so far. For example, a linear recording density of the disk, that is, recording density in the length direction of the track is increased. Or, a track width is narrowed to increase the track density, thereby improving recording density. In recent years, for further improving the recording density, there has been enthusiastically made the study and development of a contact recording in which the head is floated extremely lower or the head is brought in substantially contact with a recording medium.
On the other hand, to improve sensitivity of a signal reproduction, an active typed head, e.g., an MR head using magnetoresistive effect, has been developed. The MR head is a head, which converts a magnetic flux sent from the recording medium to an electrical signal by use of a property in which an electrical resistance of a soft magnetic member such as permalloy is changed by an outer magnetic field. The MR head converts the change of the electrical resistance of an MR element formed of the soft magnetic member to a voltage change. Due to this, the sensitivity of the signal reproduction of the head is proportional to an amount of sense currents flowing to the MR element. As a result, even if a relative speed between the head and the medium is small, a large reproducing output can be obtained. Also, by use of the feature in which the reproducing output of the MR head is large, the track width can be narrowed to improve the track density.
The reproducing head, which is formed of the MR head, is frequently used to be combined with a recording head, which is formed of an inductive head, thereby forming a composite head. In this case, the reproducing head is combined with the recording head to be spaced from each other with a predetermined distance in the track direction. The composite head is mounted on a head slider. The composite head is moved in a radial direction of the disk by a rotary actuator through the head slider. Then, the positioning to a target track, that is, the seek operation is performed. At the seek operation time, a track shift occurs between the recording head and the reproducing head due to the space existing between the recording head and the reproducing head in the direction of the track. In this case, the track shift means that the relative position between the head and the track differs by depending on the recording head and the reproducing head.
The mechanism of the track shift will be explained with reference to FIGS. 1A and 1B. FIGS. 1A and 1B are views each schematically showing a state that the composite head moved by the rotary actuator is positioned at an inner peripheral track on the magnetic disk and an outer peripheral track. As shown in the figures, for moving the composite head by the rotary actuator, an angle difference between the direction of the head (azimuth direction) and the direction of the track, that is, skew angle, is changed by depending on the track radial direction where the head is positioned. In FIGS. 1A and 1B, a skew angle .theta. is negative at the inner side (small diameter), and positive at the outer side (large diameter). The change of the skew angle appears as the track shift between the recording track and the reproducing track at it is. The track shift is increased as the track pitch is narrowed, and this brings about an obstacle to a correct reproduction.
Moreover, if the track width is narrowed to obtain high track density, it is necessary to increase the accuracy of positioning of the recording head and the reproducing head in the track width direction. However, if the track is narrowed, the tolerance between the recording head and the reproducing head in the positioning is relatively increased in view of the accuracy of the manufacturing process. This brings about an obstacle to obtain high track density.
Moreover, there is proposed a two-stage (two-dimensional) control typed head driving mechanism in which the rotary actuator is used as a coarse actuator and a mechanical fine actuator is used as a minor actuator. By use of this head driving mechanism, the composite head is controlled such that the recording head is mounted on the track at the recording time and the reproducing head is mounted on the track at the reproducing time. Due to this, for frequently repeating the recording and reproducing operations, the whole composite head must be frequently driven. As a result, it takes time to center a predetermined recording head or a reproducing head on a target track correctly.
In a case where the space between the head and the medium is extremely small and both contact with each other, its contacting force is added to the microactuator as disturbance. As a result, the head driving mechanism cannot be sufficiently functioned, and the tracking cannot be controlled with high accuracy.
Thus, in the magnetic recording/reproducing device using the composite head, there is the problem of the track shift. Then, the track shift causes the reduction of the reproducing output. Moreover, the track shift hinders the track pitch from being narrowed. Also, the track shift hinders the track density from being highly increased.